[llvm] 7f14a1d - AtomicExpand: Add NotAtomic lowering strategy

[Matt Arsenault via llvm-commits]

Author: Matt Arsenault
Date: 2022-04-06T22:34:35-04:00
New Revision: 7f14a1d46b8e2233cbfb959e55ac9b7d33449c7e

URL: https://github.com/llvm/llvm-project/commit/7f14a1d46b8e2233cbfb959e55ac9b7d33449c7e
DIFF: https://github.com/llvm/llvm-project/commit/7f14a1d46b8e2233cbfb959e55ac9b7d33449c7e.diff

LOG: AtomicExpand: Add NotAtomic lowering strategy

Currently LowerAtomics exists as a separate pass which blindly
replaces all atomics. Add a new lowering strategy option to eliminate
the atomics which the target can control on a per-instruction level.

Added: 
    

Modified: 
    llvm/include/llvm/CodeGen/TargetLowering.h
    llvm/lib/CodeGen/AtomicExpandPass.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/include/llvm/CodeGen/TargetLowering.h b/llvm/include/llvm/CodeGen/TargetLowering.h
index a2ca4595c32b8..ca60a3861b64e 100644
--- a/llvm/include/llvm/CodeGen/TargetLowering.h
+++ b/llvm/include/llvm/CodeGen/TargetLowering.h
@@ -257,6 +257,10 @@ class TargetLoweringBase {
     BitTestIntrinsic, // Use a target-specific intrinsic for special bit
                       // operations; used by X86.
     Expand,           // Generic expansion in terms of other atomic operations.
+
+    // Rewrite to a non-atomic form for use in a known non-preemptible
+    // environment.
+    NotAtomic
   };
 
   /// Enum that specifies when a multiplication should be expanded.

diff  --git a/llvm/lib/CodeGen/AtomicExpandPass.cpp b/llvm/lib/CodeGen/AtomicExpandPass.cpp
index 05b140b8174e9..dbf49fc53e10c 100644
--- a/llvm/lib/CodeGen/AtomicExpandPass.cpp
+++ b/llvm/lib/CodeGen/AtomicExpandPass.cpp
@@ -47,6 +47,7 @@
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Target/TargetMachine.h"
+#include "llvm/Transforms/Utils/LowerAtomic.h"
 #include <cassert>
 #include <cstdint>
 #include <iterator>
@@ -412,6 +413,9 @@ bool AtomicExpand::tryExpandAtomicLoad(LoadInst *LI) {
     return expandAtomicLoadToLL(LI);
   case TargetLoweringBase::AtomicExpansionKind::CmpXChg:
     return expandAtomicLoadToCmpXchg(LI);
+  case TargetLoweringBase::AtomicExpansionKind::NotAtomic:
+    LI->setAtomic(AtomicOrdering::NotAtomic);
+    return true;
   default:
     llvm_unreachable("Unhandled case in tryExpandAtomicLoad");
   }
@@ -424,6 +428,9 @@ bool AtomicExpand::tryExpandAtomicStore(StoreInst *SI) {
   case TargetLoweringBase::AtomicExpansionKind::Expand:
     expandAtomicStore(SI);
     return true;
+  case TargetLoweringBase::AtomicExpansionKind::NotAtomic:
+    SI->setAtomic(AtomicOrdering::NotAtomic);
+    return true;
   default:
     llvm_unreachable("Unhandled case in tryExpandAtomicStore");
   }
@@ -635,6 +642,8 @@ bool AtomicExpand::tryExpandAtomicRMW(AtomicRMWInst *AI) {
     TLI->emitBitTestAtomicRMWIntrinsic(AI);
     return true;
   }
+  case TargetLoweringBase::AtomicExpansionKind::NotAtomic:
+    return lowerAtomicRMWInst(AI);
   default:
     llvm_unreachable("Unhandled case in tryExpandAtomicRMW");
   }
@@ -1536,6 +1545,8 @@ bool AtomicExpand::tryExpandAtomicCmpXchg(AtomicCmpXchgInst *CI) {
   case TargetLoweringBase::AtomicExpansionKind::MaskedIntrinsic:
     expandAtomicCmpXchgToMaskedIntrinsic(CI);
     return true;
+  case TargetLoweringBase::AtomicExpansionKind::NotAtomic:
+    return lowerAtomicCmpXchgInst(CI);
   }
 }